Alp Mehmet, a Cyprus-born former diplomat who acts as vice chairman for Migration Watch UK, said: “Employers will not face a ‘cliff edge’ over their workers from the EU.

“In the past 10 years, very many migrants from Eastern Europe in low-skilled work seem to have stayed on so there is no sign that continued large inflows are needed to maintain the present number available for work.

“Cutting out this aspect of migration in future should reduce net migration by about 100,000 a year. This would be a major step forward in the Government’s efforts to reduce immigration.”

Theresa May remains committed to her predecessor David Cameron’s stated goal of reducing UK net immigration from the hundreds of thousands to the tens of thousands, although the annual inflow remains near an all-time high at 335,000.

Migration Watch UK said net immigration might actually be as much as 50,000-a-year higher than the Government claims due to what it describes as “serious deficiencies in the International Passenger Survey data on which its figures are currently based”.

The group claimed the Commons Public Administration Select Committee has admitted the figures were “little better than a best guess”.

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Continued cooperation with the EU to tackle terrorism and international crime.

Migration Watch UK also highlighted Bank of England data which suggests large-scale importation of low-skilled migrants has allowed employers to hold down pay for people in working-class occupations.

The Financial Times reports an alleged reduction in the number of EU migrants since the Brexit vote is already forcing employers in the farm and food production sectors to compete for workers, citing one poultry farmer who has had to increase wages by 15 per cent to increase his attractiveness.